1. Field of the Invention
The present invention relates to implantable spinal fixation systems for the surgical treatment of spinal disorders. More particularly, this invention relates to a transverse rod connector clip for connecting cylindrical rods to each other.
2. Background of the Invention
For years doctors attempted to restore stability to the spine by fusion (arthrodesis) of the problem area. This treatment yielded marginal results due to the inherently flexible spinal column. Over the past ten years spinal implant systems have been developed to add stability to the spine to enhance the arthrodesis rates. Such systems often include spinal instrumentation having connective structures such as a pair of plates and/or rods which are placed on opposite sides of the portion of the spinal column which is intended to be fused. These spinal systems consist of screws and hooks for segmental attachment to the spine and longitudinal rods connected to screws or hooks. These components provide the necessary stability both in tension and compression yet yield minimal torsional control.
It has been found that when a pair of spinal rods are fastened in parallel on either side of the spinous process, the assembly can be significantly strengthened by using at least one additional rod to horizontally bridge the pair of spinal rods. A cross brace assembly is disclosed in U.S. Pat. No. 5,084,049. Devices such as these commonly consist of a threaded rod for providing the desired lateral support. The threaded rod is fastened to each of the spinal rods by clamps located on each end of the threaded rod. However, this configuration is bulky and can cause irritation of the patient""s back muscles and other tissue which might rub against the device. A cross brace assembly that fits closer to the spine, preferably in the same general plane as the vertical spinal rods, would reduce the complications associated with bulkier devices.
Most existing transverse connectors consist of rods, plates, and bars linked to the longitudinal rods by coupling mechanisms with set screws, nuts, or a combination of each. These connectors require several components and instruments to build the constructs. Each additional component or instrument required to assemble the connectors adds to the xe2x80x9cfiddle factorxe2x80x9d of the surgical technique. Examples of these transverse connectors include Tranverse Link Device (DLT) and Crosslink manufactured by Sofamor Danek, Trans-Connector manufactured by Synthes, and Modular Cross Connector and Transverse Rod Connector (TRC) manufactured by AcroMed.
Telescopic rod to rod couplers for use in a spinal implant systems have also been described. Prior to the locking member being engaged, the telescoping sections may be easily slid past their extremes and out of engagement with one another. While this is a convenient method of connecting and disconnecting the coupler sections, it can be inconvenient during surgery if the sections accidentally disengage. U.S. Pat. No. 5,275,600 describes a telescopic rod to rod coupler in which the telescopic rod sections are assembled together using a 180 degree twisting motion. This is designed to minimize the risk of the rod sections accidentally disconnecting during the implant procedure.
Presently available spinal fixation systems frequently require careful alignment of the hardware used to connect the components of the spinal instrumentation with each other. A need has thus arisen for improved rod connectors to transversely connect spinal rods without requiring additional manipulation of the spinal instrumentation and to minimize the use of pedicle screws while at the same time reducing requirements to assemble small pieces of hardware during the surgical procedure.
The present invention is directed to transverse connector clips for connecting cylindrical rods in spinal fixation systems. The transverse connector clips of the present invention have a clip body with a first side and a second side. The first side of the clip body has a longitudinal axis and a pair of mirror image hemi-cylindrical shells. The hemi-cylindrical shells each have an inner diameter that is slightly smaller than the outer diameter of the cylindrical spinal rod. The clip body is shaped to allow the hemi-cylindrical shells to spread around the cylindrical rod when it is inserted between the hemi-cylindrical shells. The deflection of the hemi-cylindrical shells and the inner shell diameter allow the clip body to securely clamp on the cylindrical spinal rod, placing the inserted cylindrical rod at a 90xc2x0 angle relative to the longitudinal axis of the clip body
The transverse connector clips of the present invention can be used to transversely connect spinal rods without requiring additional manipulation of the spinal instrumentation. Because the clips of the present invention do not require any additional locking mechanism, they reduce the assembly of small pieces of hardware during the surgical procedure.